The course first summarizes the various configurations of different rotary-wing aircraft and the simple methods to calculate their performance. Methods for designing efficient rotors are explained and justified. In particular the optimization codes for airfoil and blade determination are described. The rotor design can be improved by using advanced three dimensional aerodynamics codes, whose actual possibilities are presented. Detailed papers concern the consequences of specific aerodynamic phenomena such as rotor wake on blade airloads and on rotor noise production. The state of the art of fuselage aerodynamics and on the problems related to rotor wake and fuselage interactions is given. An important part of the course is also devoted to the experimental methods used for wind-tunnel and flight tests, that are at our disposal in order to understand correctly the physical phenomena involved, and to acquire reliable data necessary for code validation.